1. Field of the Invention
Embodiments of the present invention relate, in general, to inducing sleep and more particularly to inducing an individual to a sleep state using binaural acoustic tones.
2. Relevant Background
Over 40 million people in the United States alone suffer from sleep problems. And almost everyone occasionally suffers from short-term insomnia. Sleep disorders and insomnia can result from stress, jet lag, diet, or many other factors. Insomnia almost always affects job performance and wellbeing the next day and its occurrence tends to increase with age. Some 40 percent of women and 30 percent of men are impacted by sleep disorders.
Sleeping pills are the first line of defense for short-term insomnia. Most sleeping pills stop working after several weeks of nightly use, however, and long-term use can actually interfere with good sleep. Mild insomnia often can be prevented or cured by practicing good sleep habits such as relaxing before trying to go to sleep, taking a hot bath, reading a book, winding down, etc. For more serious cases of insomnia, researchers are experimenting with light and sound therapy to alter circadian cycles.
Any amount of sleep deprivation will diminish mental performance. Indeed one complete night of sleep deprivation can be as impairing in simulated driving tests as a legally intoxicating blood-alcohol level. Moreover, people who regularly do not get enough sleep can become less sensitive to insulin and other medications.
Just as the lack of sleep can diminish a person's wellbeing and pose serious health risks, there are well known benefits to gaining adequate sleep. For example, it is well known that growth hormones in children are secreted during sleep, and chemicals important to the immune system are secreted during sleep. Studies have shown that a person can become more prone to disease if they do not receive enough sleep.
No one really knows why animals (humans) sleep. One theory is that sleep gives the body a chance to repair muscles and other tissues, replace aging or dead cells, etc. Sleep, it is believed, gives the brain a chance to organize and archive memories. Dreams are thought by some to be part of this process. Sleep also lowers our energy consumption, so we need three meals a day rather than four or five. While through the use of technology we have, as a species, become more and more adept to working in the night, humans are fundamentally diurnal. One theory is that our body is simply programmed to preserve energy until the sun comes up.
Until the 1950s, most people thought of sleep as a passive, dormant part of one's daily life. Research has determined that a human's brain is very active during sleep. Nerve-signaling chemicals called neurotransmitters control whether one is asleep or awake by acting on different groups of nerve cells, or neurons, in the brain. Neurons in the brainstem, which connects the brain with the spinal cord, produce neurotransmitters such as serotonin and norepinephrine that keep some parts of the brain active during waking moments. Other neurons at the base of the brain begin signaling during the transition from being awake to being asleep. These neurons appear to “switch off” the signals that keep us awake. Research also suggests that a chemical called adenosine builds up in our blood while we are awake and causes drowsiness. This chemical gradually breaks down while we sleep.
While asleep, an individual usually passes through five phases of sleep: stages 1, 2, 3, 4, and REM (rapid eye movement) sleep. These stages progress in a cycle from stage 1 to REM sleep, then the cycle starts over again with stage 1. We spend almost 50 percent of our total sleep time in stage 2 sleep, about 20 percent in REM sleep, and the remaining 30 percent in the other stages. Infants, by contrast, spend about half of their sleep time in REM sleep.
During stage 1, which is light sleep and associated with theta waves, an individual drifts in and out of sleep and can be awakened easily. During this stage eyes move very slowly and muscle activity slows. People awakened from stage 1 sleep often remember fragmented visual images. Many also experience sudden muscle contractions called hypnic myoclonia, often preceded by a sensation of starting to fall. When a person enters stage 2 sleep, eye movements stop and brain waves (fluctuations of electrical activity that can be measured by electrodes) become slower, with occasional bursts of rapid waves called sleep spindles. In stage 3, extremely slow brain waves called delta waves begin to appear, interspersed with smaller, faster theta waves. By stage 4, the brain produces delta waves almost exclusively and it is very difficult to wake someone during stages 3 and 4, which together are commonly referred to as deep sleep. There is no eye movement or muscle activity during this stage of sleep. People awakened during deep sleep do not adjust immediately and often feel groggy and disoriented for several minutes after they wake up. It is in this stage that children experience bedwetting, night terrors, or can sleep walk.
When a person switches into REM sleep, their breathing becomes more rapid, irregular, and shallow, their eyes jerk rapidly in various directions, their limb muscles become temporarily paralyzed, the heart rate increases and blood pressure rises. And when people awaken during REM sleep, they often describe bizarre and illogical tales—dreams.
Each of these stages or states of consciousness is also associated with specific amount of brain activity. By attaching an electroencephalograph to a person's head you can record the person's brainwave activity. An awake and relaxed person generates alpha waves, which are consistent oscillations at about 10 cycles per second. An alert person generates beta waves, which are about twice as fast.
Beta waves typically range between 12 and 40 hertz (hz). This is generally the mental state most people are in during the day and most of their waking lives. Usually, this state in itself is uneventful but it is important. Many people lack sufficient beta activity, which can cause mental or emotional disorders such as depression and insomnia. And low beta wave production (a sub-range of beta at 12-15 hz) may be related to insomnia and according to one theory stimulating beta activity can improve emotional stability, energy levels, attentiveness and concentration, as well as the ability to fall asleep. Simply put, an individual that is mentally exhausted may find it easier to fall asleep.
Conversely alpha waves predominantly originate from the occipital lobe during wakeful relaxation with closed eyes. Alpha waves are reduced with open eyes, drowsiness and sleep. Historically, they were thought to represent the activity of the visual cortex in an idle state. More recent papers have argued that they inhibit areas of the cortex not in use, or alternatively that they play an active role in network coordination and communication. Occipital alpha waves during periods of eyes closed are the strongest EEG brain signals.
Alpha waves, 8-13 hz, are associated with being awake but relaxed and not processing much information. When a person gets up in the morning, and just before sleep, they are naturally in this state. The brain automatically starts producing more alpha waves when the eyes are closed.
Theta waves, which are characterized from 3-8 hz appears to be a transitional state of light sleep or extreme relaxation. Brain activity producing delta waves 0.2-3 hz is accepted by most studies as being asleep. Delta waves are the slowest, but highest amplitude brainwaves. Delta waves begin to appear in stage 3 sleep, but by stage 4 nearly all spectral activity is dominated by delta waves. Stage 3 sleep is defined as having less than 50% delta wave activity, while stage 4 sleep has more than 50% delta wave activity. Delta waves occur in all mammals, and potentially in all animals as well.
While scientists can validate through devices such as an EEG that when an individual is relaxed or asleep they produce alpha or delta waves respectively assisting one to arrive at that state remains a challenge. Sleep remains for many an illusive goal keeping the treatment of insomnia a major focus of many research laboratories and commercial markets. These and other challenges with respect to the treatment of insomnia and other sleep disorders are address by one or more embodiments of the present invention.
Additional advantages and novel features of this invention shall be set forth in part in the description that follows, and in part will become apparent to those skilled in the art upon examination of the following specification or may be learned by the practice of the invention. The advantages of the invention may be realized and attained by means of the instrumentalities, combinations, compositions, and methods particularly pointed out in the appended claims.